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TB rebuild, now its running very rich!

ANDYVH

New member
I just did the Bing TB rebuild on my 94 R1100RS, at 146,000 miles. Replacing the parts was fairly easy, just make sure you install the butterfly plate in the correct orientation, exactly like the factory setup, with the number facing to the rear of the throat and up to the top. I installed the new shaft assembly, then slid the plate into the shaft and aligned it, then installed the screws but not tight. Then I moved the throttle cam to settle the plate into the bore. Then applied Loctite to the screws and tightened the plates in place on the shafts.

When I took the left TB apart, I was careful to not turn the TPS. But when I reinstalled it something must have changed. Now the bike runs rich, my fuel mileage has dropped 10 miles per gallon, and the bike loads up at idle, big time. I balanced the TBs with my mercury sticks, until I get a chance to get my bike to the local BMW shop. The balance off idle is good, and throttle response is good, but fuel mileage that used to regularly be mid 40's is dropped WAY off.

Oh, the RH TB shaft had minimal wear, but I can see/feel it. So that accounted for the "thuk, thuk, thuk" I heard at idle. And the big brass screws are now near equal in position where before the RH one was turned almost all the way in, indicating an air leak I assume.
 
Sounds like it's time for Rob Lentini's ZERO - ZERO procedure to make sure the TPS offset voltage is correct.
- Make sure zero TPS really is zero TPS
- Set offset voltage
- Set basic idle air screw setting
- Balance at idle
- Balance at 3K and 5K RPM

That's how I did mine after breaking the taboo blue loctite BMW seal on the throttle body stop settings.

Section III, Page 79 of this document:
http://www.ibmwr.org/r-tech/oilheads/R11Manual/Oilhead_Maintenance_2-25-02.pdf
 
I got out in the garage tonight and checked the TPS output signal at the red/white wire to ground. It was at 1.435v as I had reinstalled the TPS after I had installed the new shaft assembly. So that confirms the very rich running it was doing.

I adjusted the signal down to .395v and the bike almost instantly idled normally. I went through the TB balance as best I could with my mercury sticks. This weekend I'll do it even better using the BMW shop electronic manometer. The bike runs near normal now and idles right down to a steady tickover right off the throttle.
 
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